The invention relates to fixed ratio planetary type traction roller transmissions whose traction surfaces are in engagement with each other for the transmission of motion therebetween.
There are generally provided axial cam structures which generate axial forces dependent on the torque transmitted through the transmission and the axial forces so generated are applied to conical race rings or conical sun structures to provide the appropriate traction surface contact forces.
An arrangement in which the traction ring consists of two slightly conical rings which are forced toward each other to engage the traction rollers therebetween is shown for example in U.S. Pat. No. 4,052,915. Applicant's published manuscript "Bearings and Rolling Traction, Analysis and Design" which is available from Excelermatic, Inc., Austin, Tex. 78731, describes and shows in FIG. 20-3a fixed ratio traction roller transmission in which the sun consists of two slightly conical sun sections which are forced toward each other to engage the traction rollers for firm torque-dependent engagement of the traction rollers with the traction ring and the sun structure.
Australian Pat. No. 16,391, Italian Pat. No. 494,348 and U.S. Pat. No. 3,375,739 show planetary type traction roller transmissions including sun rollers, traction rings and planetary traction rollers which are conical and so arranged that their axes and all tangential axial lines of the traction surfaces intersect on the axis of the transmission and means are provided for forcing the planetary rollers into engagement with the suns and the traction rings.
The means providing the engagement forces are generally torque dependent so as to provide the appropriate engagement forces or they are structures which provide fixed forces especially if the torque to be transmitted through the transmission during its operation does not substantially vary.
For generating torque-dependent engagement forces there are usually provided axial cam structures or there may be provided hydraulic engagement force generating means which require a pressurized fluid control structure in order to supply the appropriate engagement forces.
Both arrangements are expensive. There are however certain applications, for example, in torpedo drives, where a traction roller transmission is advantageous because of its quiet operation but where costs should also be maintained as low as possible since the transmission is destroyed with the actual use of the torpedo. A preload corresponding to the maximum torque which can be achieved very inexpensively would also be quite adequate since a torpedo transmission is operated only for a short time and during all that time essentially at a predetermined torque.
Torpedoes however are stored for long periods of time until they are actually used and keeping the transmission's traction surfaces under the preload as required for operation will, in time, cause denting and corrosion of the traction surfaces which results in noisy operation or even failure.
Transmissions of the above type have relatively small cone angles in order to avoid the need for large axial engagement forces and therefore they require relatively large axial travel for the engagement member--when forced toward the other members, for example by a hydraulic piston--from a contact force-free position to a position in which the appropriate contact forces as needed for the transmission of the needed torque are generated.
Also inappropriately large forces applied to the engagement member may damage the rollers' traction surfaces because the relatively small cone angles translate the engagement forces in large surface contact pressures. It is therefore the principal object of the present invention to provide a transmission whose traction rollers have relatively small cone angles in order to be able to be operated by only small axial engagement forces but which nevertheless can be operated by any available force generating structure without the danger of damage to the traction surfaces. It is also desirable that, in spite of the relatively small cone angles of the traction surfaces, only a relatively small amount of axial movement is required for the achievement of the required traction roller surface engagement.